Application of rhizobacteria for induced resistance

This article provides a review of experiments conducted over a six-year per iod to develop a biological control system for insect-transmitted diseases in vegetables based on induced systemic resistance (ISR) mediated by plant growth-promoting rhizobacteria (PGPR). Initial experiments investigated the factors involved in treatment with PGPR led to ISR to bacterial wilt disea se in cucumber caused by Erwinia tracheiphila. Results demonstrated that PG PR-ISR against bacterial wilt and feeding by the cucumber beetle vectors of E. trachiphiela were associated with reduced concentrations of cucurbitaci n, a secondary plant metabolite and powerful beetle feeding stimulant. In o ther experiments, PGPR induced resistance against bacterial wilt in the abs ence of the beetle vectors, suggesting that PGPR-ISR protects cucumber agai nst bacterial wilt not only by reducing beetle feeding and transmission of the pathogen, but also through the induction of other plant defense mechani sms after the pathogen has been introduced into the plant. Additional green house and field experiments are described in which PGPR strains were select ed for ISR against cucumber mosaic virus (CMV) and tomato mottle virus (ToM oV). Although results varied from year to year, field-grown tomatoes treate d with PGPR demonstrated a reduction in the development of disease symptoms , and often a reduction in the incidence of viral infection and an increase in tomato yield. Recent efforts on commercial development of PGPR are desc ribed in which biological preparations containing industrial formulated spo res of PGPR plus chitosan were formulated and evaluated for use in a transp lant soil mix system for developing plants that can withstand disease attac k after transplanting in the field.